This invention relates to the utilization of blends of plant protein with poly(lactic acid) (or polylactide, PLA) for biodegradable plastics. This invention also relates to the utilization of blends of plant protein with polycaprolactone and modified poly(ethylene terephthalate) for biodegradable plastics. The invention also relates to the utilization of blends of plant protein with poly(vinyl alcohol) and N-vinyllactam polymers.
The majority of plastics are petroleum-based, and therefore non-biodegradable. The vast amount of waste generated through use of traditional plastics is becoming a burden on local landfills. There is, therefore, a growing interest in using renewable resources to replace or partially replace petroleum-based plastics.
The main attractive features of soy protein-based plastics are their biodegradability and the fact that soy is an abundant renewable resource. In fact, soy protein polymers have been suggested as inexpensive and environmentally-friendly substitutes for use in: packing materials; insulation; dishware; utensils; clam shell containers; golf tees and other outdoor sporting goods. U.S. Pat. No. 5,523,293 to J. Jane and S. Wang, discloses compositions of soy protein-based biodegradable plastics which are said to be useful for molded materials. The formulation is generally composed of soy protein (SP) (or SP/starch), a carbohydrate filler, a reducing agent, a plasticizer, water, and optional additives. U.S. Pat. No. 5,665,152 to Sukh Bassi discloses the compositions of blends of grain protein (wheat gluten or corn gluten) with starch. The compositions are said to be useful for molded plastics. U.S. patent Ser. No. 5,710,190, there is disclosed a soy protein polymer comprising soy protein, a filler (polysaccharide material, i.e. starch, gum and cellulose-based materials), a foaming agent, and plasticizers.
There are several limitations for broad application of soy protein and starch plastics described previously. The main problems include environmental instability and poor water resistance. Moreover, the plastic products made from SP and starch become brittle when moisture is lost, despite retention of high tensile strength. In contrast, the mechanical properties of SP/starch plastics deteriorate upon exposure to slight moisture increases, such as a change in relative humidity.
Alternate solutions have been proposed to solve these problems, including chemical modification, coating and blending with synthetic polymers. Usually, the benefit of chemical modification of biopolymers is offset by the decrease in product biodegradation and the increase in cost. Furthermore, coated soy protein plastics have not proven economical compared to petroleum-based plastics. To make soy protein plastics more economical, researchers have resorted to blending biopolymers with synthetic polymers. U.S. Pat. No. 5,321,064 to U. Vaidya and M. Bhattacharya, discloses compositions of biodegradable plastics made by reactive blending of a synthetic polymer with a naturally-occurring biodegradable polymer. These synthetic polymers contain functional groups which can form covalent bonds between two polymers. In other aspects of the Vaidya patent, gluten and maleic anhydride-modified polycaprolactone was blended. The blend with polycaprolactone became quite soft when subjected to a temperature above 60xc2x0 C.
Other alternatives have been discussed in Li et al. The effects of Specific Interactions on the Surface Structure and Composition of Miscible Blends of Poly(vinyl alcohol) and Poly(N-vinyl pyrrolidone). Polymer, 1998, 39(11) 2355 and Raghunath et al. Grafting of Poly(vinyl pyrrolidone) onto Gelatin and its Applications as Synthetic Plasma Expander. Eur. Polym. J. 1985, 21(2), 195.
Citation of the above documents is not intended as an admission that any of the foregoing is pertinent prior art. All statements as to the date or representation as to the contents of these documents is based on subjective characterization of information available to the applicant, and does not constitute any admission as to the accuracy of the dates or contents of these documents.
It is therefore an object of the present invention to provide soy protein plastics which have the advantage of being water resistant, biodegradable, wherein the biodegradation results in environmentally-inoffensive compounds.
It is a further object to provide biodegradable composites with added strength.
It is yet another object to provide biodegradable composites with added strength and water resistance.
It is an object to provide soy protein/polylactide composites.
It is also an object to provide soy protein/polylactide/compatibilizer composites.
It is a specific object to provide soy protein/polylactide/poly(2-ethyl-2-oxazoline) composites.
It is an object to provide soy protein/polycaprolactone and modified poly(ethylene terephthalate) composites.
It is a specific object to provide soy protein/polycaprolactone/modified poly(ethylene terephthalate)/poly(2-ethyl-2-oxazoline) composites.
It is also an object to provide plant protein/poly(vinyl alcohol)/N-vinyllactam polymer composites.
It is also a specific object to provide plant protein/poly(vinyl alcohol) and poly(N-vinyl pyrrolidone) polymer composites.
Finally, it is an object of the invention to provide methods of making the composites.
Definitions. For the purposes of the present invention, the following terms shall have the following meanings:
xe2x80x9cPlant proteinxe2x80x9d means any compound comprising a protein (any compound comprising amino acids, including, for example, polypeptides, peptides and modifications of nascent proteins, such as glycosylations, or cleavage products), wherein the protein is or was derived from plant matter, including a full plant, or derivatives from seeds, leaves, stems, roots, or any other plant parts or extractions.
xe2x80x9cCompatibilizerxe2x80x9d means any compound capable of enhancing the interaction between a plant protein and a polylactide, a plant protein and a polycaprolactone and/or modified poly(ethylene terephthalate).
xe2x80x9cPolylactidexe2x80x9d means the compound described herein as xe2x80x9cpolylactidexe2x80x9d, as well as any compound which functions in the same way with the same result. For instance, modified polylactides, acids thereof (e.g. polylactic acid) or mimetopes are within the present definition.
xe2x80x9cPolycaprolactonexe2x80x9d means the compound described herein as xe2x80x9cpolycaprolactonexe2x80x9d, as well as any compound which functions in the same way with the same result. For instance, modified polycaprolactone, acids thereof, or mimetopes are within the present definition.
xe2x80x9cModified poly(ethylene terephthalate)xe2x80x9d means the compound described herein as xe2x80x9cpoly(ethylene terephthalate)xe2x80x9d, as well as any compound which functions in the same way with the same result. For instance, modified poly(ethylene terephthalate), acids thereof or mimetopes are within the present definition.